The present invention relates to an improved process for the preparation of urethanes by reacting primary amines, alcohols, and organic compounds which have carbonyl groups. N-unsubstituted urethanes and optionally N-mono- or N,N'-disubstituted ureas or polyureas are used as the organic compounds having carbonyl groups.
N,O-disubstituted urethanes may be prepared by reacting organic isocyanates with alcohols. This reaction is reversible, i.e., the urethanes, once produced, can be thermally dissociated into the isocyanate and the alcohol from which they were derived. One such dissociation reaction is described in U.S. Pat. No. 2,409,712. Urethanes which can be thermally dissociated into isocyanates are, therefore, potential starting materials for the preparation of these isocyanates. Until now, such isocyanates had been almost universally prepared by reaction of primary amines with phosgene. The preparation of urethanes without the use of phosgene in a manner which avoids subsequent thermal dissociation of the product urethane would, however, provide a valuable alternative to the commercially used process.
Urethanes have been prepared without phosgene by reacting urea with amines and alcohol (see, for example, U.S. Pat. Nos. 2,409,712 or 2,806,051). However, these prior art processes produce urethanes in insufficient amounts and in an impure form.